Conventionally, microfabrication by lithography using photoresist compositions has been performed in the production of semiconductor devices. This microfabrication is a fabrication method that includes forming a thin film of a photoresist composition on a substrate to be fabricated such as a silicon wafer, radiating active rays such as ultraviolet rays onto the thin film through a mask pattern in which a pattern of a semiconductor device is formed, developing the film, and etching the substrate to be fabricated such as a silicon wafer using the obtained photoresist pattern as a protective film. In recent years, higher integration of semiconductor devices has been pursued, and there is a trend for the active rays used to have shorter wavelengths from KrF excimer lasers (248 nm) to ArF excimer lasers (193 nm). This trend has been accompanied by significant issues of effects due to standing waves and diffuse reflection of the active rays from the substrate. Accordingly, methods have been extensively studied that include providing an anti-reflective coating (Bottom Anti-Reflective Coating, BARC) between the photoresist and the substrate to be fabricated.
When a finer resist pattern is further pursued, an issue of resolution and an issue in which the resist pattern collapses after development may occur, and thus thinner resists are required. This makes it difficult to achieve sufficient resist pattern film thickness for fabrication of a substrate, and thus a process has become necessary in which the function of a mask during the substrate fabrication is imparted not only to the resist pattern, but also to a resist underlayer film that is formed between the resist and a semiconductor substrate to be fabricated. As a resist underlayer film for such a process, unlike a conventional resist underlayer film having a high etching-rate property (high etching rate), a resist underlayer film for lithography having a selection ratio of dry etching rate that is close to that of the resist, a resist underlayer film for lithography having a selection ratio of dry etching rate that is smaller than that of the resist, or a resist underlayer film for lithography having a selection ratio of dry etching rate that is smaller than that of the semiconductor substrate is required.
Examples of a polymer for the resist underlayer film described above include the followings.
Resist underlayer film-forming compositions each including polyvinyl carbazole are exemplified (see Patent Document 1, Patent Document 2, and Patent Document 3).
A resist underlayer film-forming composition including a fluorene phenol novolak resin is disclosed (see Patent Document 4, for example).
A resist underlayer film-forming composition including a fluorene naphthol novolak resin is disclosed (see Patent Document 5, for example).
Resist underlayer film-forming compositions each containing fluorene phenol and aryl alkylene as repeating units are disclosed (see Patent Document 6 and Patent Document 7, for example).
A resist underlayer film-forming composition including carbazole novolak is disclosed (see Patent Document 8, for example).